It is known in the art to provide a valve for metering a fluid such as fuel using a solenoid arrangement, whereby supply of current to the coil of the solenoid causes an armature to move relative to the coil. This in turn may displace a spool which meters the flow of fuel.
An electromechanical fuel metering valve may be used for dispensing fuel to the combustion zone of an engine, e.g., a gas turbine engine of an aircraft. Valves such as these are one of the components of an aircraft fuel control system and can be integrated with injector nozzles which spray the fuel into the combustion zone.
A problem of the design of such direct drive metering valves is a loss in flow adjustability, due to non-linearity of the solenoid current-armature displacement characteristic as the armature moves along its stroke. This is particularly so when other factors like changes in temperature have to be accounted for. As a result, the small-sized solenoids, which need to generate sufficiently high forces against a return spring in the valve, have a range of linearity limited to few tenths of a millimetre.
It would therefore be beneficial to develop an improved metering valve with more precise metering and adjustability. It would also help if more of the armature stroke could be used during valve operation.
U.S. Pat. No. 4,793,313 discloses a fuel injection apparatus for internal combustion engines, which uses a transducer to detect the switching and movement time of a valve member of a valve. By measuring these timings, the apparatus can determine how much fuel has been injected based on the amount of time the valve has been open. The apparatus can thus ensure that an intended quantity of fuel is supplied to the injectors, taking into account the movement time and the time taken for the valve to switch to the open or closed positions.
U.S. Pat. No. 5,270,900 discloses a method similar to the above. The method involves supplying a voltage to the armature measuring the current flow and calculating from the current flow and the voltage supplied when the movement of the armature began. Using the timings, the apparatus will then stop supplying voltage to the circuit a predetermined time after the motion was deemed to have begun.
U.S. Pat. No. 4,251,762 discloses an apparatus for sensing the actual position of an armature in an electromagnetic driver such as a solenoid. The apparatus does so using an electromagnetic induction loop, i.e. using inductors, to sense the position of the armature. Further, this document mentions that other methods may be used for measurement, such as by attaching a capacitor plate to the armature, for example. This document then explains that such an arrangement would be disadvantageous for at least the reason that the capacitor plate adds a significant mass to the armature.
The above methods and systems provide some possibilities for measuring armature position and for controlling metering. However, further improvements are proposed in the present disclosure.